Effects of flow incidence on aerothermal performance of transonic blade tip clearance flows

•New physical insights of transonic blade tip flow mechanisms are proposed.•We examine effects of flow incidence on transonic tip aerothermal characteristics.•Flow incidence effect on tip leading-edge aerothermal performance is more evident.•Flow incidence effects at 0.4% tip gap are smaller than that at 1.0% tip gap.•Optimal transonic blade tip design suggested for enhanced aerothermal performance.

This paper is a continuation of the previous work and aims to understand how the inlet incidence flows influence the transonic tip leakage loss-generation processes and overtip heat-transfer. Five incidences ranged from −15 to 15°, and two tip gaps of 0.4% and 1.0% of blade span are investigated. Numerical calculations have been carried out by means of the ANSYS-CFX calculation tool, using the k-ε SST turbulence model to study the sensitivities of transonic blade tip aerothermal performance to flow incidences in an RT27a linear turbine-cascade. Flow patterns over the transonic blade tip at design incidence, overtip flow fields and aerodynamics sensitivity to flow incidence, and transonic tip heat transfer characteristics at different incidences are investigated. The computed results show a fair agreement with the rig data and show that the effects of flow incidence on aerodynamics and heat transfer in the front part of blade tips are bigger than that in the rear part of blade tips, and flow incidence effects at 0.4% tip gap is smaller than that at 1.0% tip gap. At various incidences, as the tip gap height increases, the shockwave reflections become more obvious, and it hence reduces the leakage flow. However, the large tip clearance height induces elliptical TLV core structure, and leads to strong mixing with the mainflow. For the blade-tip trailing-edge flow regions, at two blade tip gaps the overtip heat transfer decreases normally as the incidence increases.